


Four times Sherlock blamed Mycroft and one time when Sherlock really was to blame

by SStar



Category: Sherlock (TV), Sherlock Holmes & Related Fandoms
Genre: BAMF Mycroft, Brotherly Love, Gen, Holmes Brothers' Childhood, Holmes Family, Humour, Kid Mycroft, Kid Sherlock, Kidlock, Mycroft Being a Good Brother, POV Mycroft Holmes, Protective Mycroft
Language: English
Status: In-Progress
Published: 2014-05-26
Updated: 2014-06-27
Packaged: 2018-01-26 16:13:04
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 2
Words: 4,349
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/1694465
Author URL: https://archiveofourown.org/users/SStar/pseuds/SStar
Summary: <blockquote class="userstuff">
              <p>Mycroft had made a vow to protect Queen and Country. It was only superseded by one other vow, one that had never been spoken aloud. To protect and cover for his irritating, troublesome, brilliant little brother.</p><p>From the Holmes' childhood to the present day.</p>
            </blockquote>





	1. Sherlock’s greatest discovery

**Author's Note:**

> Disclaimer: all characters belong to ACD, Moffat, Gatiss and the BBC. I own nothing but my own imagination.
> 
> Unbeta'd but edited - all mistakes are my very own.
> 
>  
> 
> _“Are you two smoking?”_  
>  _“No!” “It was Mycroft.”_  
>  **His Last Vow**

Sherlock was five when he hit upon the greatest discovery of his life. He couldn’t call it a deduction because he hadn’t learnt the art at that age.

Mycroft on the other hand considered this specific day as the day that his life changed. And not necessarily for the better.

It had been raining. For days on end. The typical Great British weather. An eternal failsafe conversation topic for strangers and friends alike.

Once, a few weeks after Sherlock had turned five, Mycroft taken it upon himself to prove the correlation between bank holidays and the local weather phenomena where he lived with Mummy and Dad. And Sherlock.

Mycroft made careful notes of his observations before he attempted to devise a formulaic structure that reflected the inherent pattern he knew lay underneath. Had acquired several of Mummy’s undergraduate textbooks in the attempt. Mycroft spent weeks on his endeavour but to no avail. The maths simply wouldn’t resolve itself into the perfect set of equations.

In a rare burst of frustration, Mycroft gathered the pages upon pages of observations and calculations, stuffed them into a plastic bag and thrown it all out. A few days later, the night before their weekly refuse collection, Mycroft decided to rescue his notes.

At the crack of dawn before anyone else would awake Mycroft crept out of his bedroom, pulling on his dressing gown and slippers as he tiptoed down the stairs. A quick glance out of the ground-floor windows made it clear the ever-present rain hadn’t abated although it had lessened to resemble a light, continuous spray. Far too light to take along an umbrella Mycroft determined.

He grabbed his coat along the way and exchanged his slippers for wellingtons at the kitchen door. Having unlocked the door leading to the garden, bracing himself for the cold, Mycroft hurried to their garden shed, next to which their bin was stationed.

Wrinkling his nose as the smell of mildew and decay sprung forth when he lifted the bin lid, Mycroft leaned over and looked in.

Just the two usual black bin bags he observed his Father empty that week. The bag he’d thrown away, a little bright blue plastic thing, was missing. Mycroft was so astonished at this inconsistency that he didn’t hear the light footsteps or the second presence until they made themselves known.

“What are you doing, Mycroft?”

_Woof woof._

Mycroft slammed the metal lid back onto the bin, wincing at the loud bang he made, and spun on his heels. There, only a few feet from him, stood Sherlock. And Redbeard – the Irish Setter puppy and his little brother were rarely seen apart. This cold, wet morning once more proving the rule.

“What are you doing up at this hour, Sherlock?” Mycroft asked. A quick glance at his brother’s apparel confirmed his suspicions.

Sherlock must have heard Mycroft sneak out and decided to follow him. An adventure for Pirate Holmes and First Mate Redbeard no doubt. The evidence spoke for itself in his brother’s creased pyjamas, the lack of thought for a coat and those pale blue eyes peeking out from under tousled curls, alight with curiosity.

At least the little imp had enough sense to pull on his own wellies before following Mycroft outside.

With a heavy sigh that spoke of his exasperation, Mycroft closed the distance to his brother, pulling his coat off at the same time. In a manoeuvre made more complicated by the wriggling limbs and mumbled complaints of Sherlock, Mycroft managed to both wrap his coat around the smaller boy and pick him up, balancing the smaller boy upon his hip.

“Sherlock,” he chastised when his damp cheek came into contact with cold skin. “You’re freezing! What on earth possessed you to come outside without a coat?”

“Couldn’t sleep.”

“Oh, Sherlock-“

“And me and Redbeard thought we’d go on an adventure!”

Mycroft huffed. “Redbeard and _I_.”

“That’s what I said,” Sherlock complained, kicking out at Mycroft. Luckily his coat prevented Sherlock from putting much force behind the movement but he was left with a partial muddy footprint on his own pyjamas.

“Sherlock!”

“Not my fault.”

“You _kicked_ me.”

“You picked me up.”

“You’re so insufferable.”

“Daddy says that’s what little brothers are supposed to be.”

“He’s just trying to make you feel better,” Mycroft replied. “But if you carry on like you are, you do realise Mummy and Daddy will send you back from where you came from.”

“No they won’t!”

“They will.”

“Liar, liar pants on fire.”

Mycroft, with a slow and exaggerated movement, made to check his pyjama bottoms. “No fire here, Sherlock.”

He held back an amused, indulgent smile at the sight of his little brother pouting. Sherlock had recently developed the habit of pushing his lower lip out momentarily when he sulked. Mycroft thought it was rather adorable really and kept a mental tally of the number of times he could induce that specific look.

A second, better aimed kick at his body found him dropping Sherlock, needing to press his palms against the pain and soon-to-be-blossoming bruises. The smaller boy, much to Mycroft’s relief, landed safely on his feet.

“Even Redbeard thinks you’re a lying liar,” Sherlock shouted at him before running towards the open kitchen door. “Come on Redbeard! Let’s leave boring Mikey alone to be a dull fart just as he likes!”

The Irish Setter raced past him barking and chasing after the giggling younger boy. With a pained sigh as Mycroft rubbed the tender skin on his left flank where his brother had hit him – he just _knew_ Sherlock would continue to be a pain in his side when the little boy grew up to become the great man Mycroft hoped he could be – he started to make his way back to the house.

He closed and locked the kitchen door behind him, his dirty wellington boots neatly placed on the mat for cleaning later – once he’d had a hot shower – when Mycroft realised something was off. Slowly turning around, the first thing that he noticed was his coat, lying in a heap at his feet.

Dumped on the kitchen floor without care nor worry. _Sherlock, you little arse._

The lower half of his coat was sodden and filthy. Mud, liquid and little clumps of glass clung to the wool from where it had obviously dragged along the garden when Sherlock had ran back into the house.

In addition, there were smaller marks leading off from coat and into the house proper. With a feeling akin to morbid curiosity Mycroft followed the trail of Redbeard’s muddy paw prints, groaning under his breath as the marks remained clear on both the stone kitchen floor and the wooden floorboards of their main room.

Their couch and coffee table both bore evidence of mud, obviously from where Redbeard had brushed against them. Exactly how the puppy became so bedraggled in mud in just a few minutes escaped Mycroft. Horror surged through him until he heard a muffled giggle coming from the corner of the room.

He stalked over to the side table and bent over. There he found both culprits huddled together. Sherlock was even dirtier than he had been just a few moments ago and the puppy’s tail appeared to be eagerly painting a canine masterpiece against the wall.

“Get up,” Mycroft hissed.

“What for?”

“Because one of us has to be sensible. I have to get the both of you upstairs and in the bath to clean you up,” he replied with a patience he was rapidly developing where Sherlock was concerned. “Before we can get back and clean the mess you and Redbeard made in here and the kitchen before Mummy sees!”

“It’s not _that_ bad!”

Mycroft snorted as he took in the sight of his little brother. With Redbeard in such close proximity to Sherlock, it was unsurprising that his pale skin and once-clean pyjamas were smudged with mud. “I assure you it is, Sherlock. Do come out from under the table.”

“No.”

“Yes.”

“No.”

Mycroft threw a glare at his younger brother as he considered a different approach. He took a few steps back and couched down. Looking both reprobates in the eye, he spoke one single word in a low, commanding tone. “ _Redbeard!_ ”

The puppy, as attached as it was to Sherlock, had not yet once failed to respond to Mycroft’s ‘ordering’ voice. The puppy broke free of Sherlock’s hold and rushed across the short distance into Mycroft’s outstretched arms. He did think it was a shame that the same tone had no effect whatsoever on his irritating little brother although the puppy’s desertion did draw Sherlock out from his hiding place.

“Right,” Mycroft announced in a smug tone. “Upstairs, _now_.”

“Give him back! Redbeard!”

“Sherlock, do behave. This is all rather unbecoming,” Mycroft chastised as all three-foot-five of Sherlock slammed into him. He gritted his teeth as the impact sent a sharp stab of pain along his left side where Sherlock had kicked him.

“God, you sound like an old grump,” Sherlock complained as he clawed at Mycroft, who held Redbeard to his chest and neck to prevent the younger boy hurting the puppy in his desperation.

He absently decided the two of them must look a right sight fighting in their main living room. Sherlock, all indignant spirit and fast-moving limbs, and Mycroft, damp-smelling and trying to maintain a façade of composure with a barking, grubby puppy between them.

He didn’t think it could get worse.

But then when a situation involved Sherlock, of course it could. And usually did.

“Morning, boys,” Mummy said as she walked into the room from the other entrance. They had missed the tell-tale sound of footsteps on the stairs with the distractions of their own argument. “You’re up early, Sherlock. Mikey, would you mind putting the fire on while I get a pot of tea on and then I can sort out some breakfa-“

Mycroft’s eyes – wide and unblinking – met his mother’s as they moved from Sherlock’s dishevelled appearance to the puppy in his arms to his own current state. It didn’t even occur to him to correct his mother on her use of nickname. Instead he waited for the inevitable explosion.

“Sherlock! Stop!” Mummy ordered. “Mikey, what is going on? What have the three of you been up to? You’re all absolutely filthy. Oh boys!”

By this point in her scolding Mummy had navigated around the furniture to the corner of the room where they had been fighting. She clucked as she rubbed at a drying spot of mud on Sherlock’s nose, much to his squirming brother’s irritation. Sighed as she plucked at Mycroft’s damp pyjamas and wisely kept well clear of the dirty Irish Setter, who seem rather content licking and nuzzling Mycroft’s face.

With her hands on her hips, Mummy gave Mycroft and Sherlock her oft-practised disapproving stare. “Now boys. Were you fighting?”

The two brothers replied at the same time. “No.” “It was Mycroft!”

Mummy huffed, throwing disappointed looks at both Mycroft and Sherlock. “The two of you will be the death of me,” she fussed. “Right. Mikey, take Redbeard and Sherlock to the bathroom and make sure they have a bath to get rid of all that dirt and then make sure you get yourself in the shower and into warm clothes, dear.”

“Yes, Mummy.”

“Sherlock, you _will_ let Mikey help you and Redbeard. No complaints! I won’t have you track dirt throughout the house.”

Sherlock scowled. “Yes,” he mumbled, clearly unhappy.

“Go on up then,” she ordered.

Sherlock didn’t move, instead glaring at Mycroft as he raised his objection. “He still has Redbeard.”

“Oh! Give him the puppy, Mikey.”

Mycroft was only too happy to hand over the puppy, practically shoved him into Sherlock’s waiting arms. After a gesture from Mummy, he watched Sherlock start to back away towards the other door through which he could get to the staircase.

“It’s far too early in the morning for this level of chaos,” Mummy grumbled after a long moment where she merely observed Mycroft. “Mikey, you’re old enough to know better. You shouldn’t start fights with Sherlock.”

“I didn’t!” he protested, acutely aware at how his cheeks flushed with shame upon his mother’s admonishment.

“But you shouldn’t get embroiled, Mikey.”

“Mycroft,” he corrected resentfully. His mother merely rolled her eyes at his correction before she bustled into the kitchen while he trudged in the same direction as Sherlock, eager to get the whole sorry mess over with and into a hot shower and warm clothes himself.

His foot had just hit the first step of the staircase when he looked up and caught a flash of Sherlock’s face before the boy spun around and ran up the final few steps. His little brother had obviously waited on the stairs to listen to Mummy’s telling off. But it was the expression on Sherlock’s face that stayed with Mycroft.

It was a look that said Sherlock had been struck with the realisation that he could always pin the blame on his older brother.

And that Mycroft, being the sentimental fool that he so obviously was, would always protect him to the best of his ability.


	2. The Elephant toothpaste plan

Mycroft tapped the tip of his fountain pen against his lower lip as he considered the question. With a controlled sigh that did nothing to soothe the internal feelings of frustration, Mycroft scrawled the Feynman diagrams that described a beta decay before moving onto the next part of the question. That he could so easily deconstruct the simplistic questions in the recently amended A-level physics question and reform it into something much more challenging was a little disappointing.

Mycroft was fully aware that his abilities surpassed the challenge of A-Levels. That he was comfortably working through second and third year university syllabus materials but appearances had to be maintained. And that mean taking his A-Levels the following summer.

Followed by the prospect of leaving his childhood home to attend Oxford University. The interview had been the most challenging intellectual exercise he’d undertaken so far although even some elements of that had been mundane. A rather frightful prospect at the tender age of seventeen. Some time away from Mummy would probably be best too.

He knew that having a genius for a son would overwhelming for any parent, having two with such different temperaments must have been a struggle even for their patient father and intelligent mother. Yet Mycroft couldn’t help feel aggrieved at his mother at her own resentment at Mycroft. That he had surpassed her in terms of logic, critical thinking, and problem solving, with his memory and planning skills.

With the exception of her own specific area of post-doctoral mathematical research. Not that Mycroft was that far behind Mummy there either, having spent many nights reading her research notes and books.

But first, Mycroft firmly reminded himself. Pass his A-levels exams. University. Then forge a career that would actually challenge and stimulate him. In London.

“Mycroft!”

And try not to strangle his impetuous, boisterous little brother, who at ten years of age knew better than to barge into Mycroft’s bedroom when he was doing his homework.

Mycroft carefully continued the curved line he had been drawing indicating a photon before branching off into the next set of subatomic particles. He spared a quick glance at his door, in whose frame Sherlock stood. “Didn’t Mummy tell you not to barge in if a door is closed? It’s considered polite to knock first and wait for an invite to enter the room.”

“Polite is a delusion of respectable human behaviour, Mycroft,” Sherlock chirped back. “Besides you never knock on my bedroom door.”

“That’s because you never close your door.”

“You still don’t knock,” Sherlock persisted with his logic. “Anyway, Mycroft. I need you to help me.”

“I’m doing my homework, Sherlock. Can’t you ask Mummy or Dad?”

“They don’t know as much as you.”

Mycroft snorted. He was waiting for the day when Sherlock decided he was too old – too proud – to ask him for help. And yet at the same time he dreaded that day and had made a self-imposed declaration to always be there for his little trouble-magnet brother. “I’m sure they’re fully capable of answering whatever questions _you’ve_ got, Sherlock.”

“They’ve gone out.”

“What?” Mycroft twisted to look at Sherlock. “When?”

Sherlock shrugged. “Dunno.”

“I _don’t_ know.”

“Mikey!”

“Mycroft,” he corrected. “If you could be so kind as to take on board and exact just one thing in your life, Sherlock, please let it be the full and proper use of the English language. Words are your first, and in some cases will be your only, weapon in this world.”

“I _don’t_ know,” Sherlock mimicked with a theatrical roll of his eyes. “So will you help me?”

Mycroft turned back to his homework, moving onto the next question about the double-slit experiment. “What is it that you want then?”

“How much water do I need to make a saturated solution of potassium iodide?”

“Why do you need to know that?” Mycroft asked as he began to note down the basic set-up to observe wave-particle duality in his exercise book.

He ignored the clear huff before Sherlock spoke. “My form teacher is an idiot.”

“In what regards this time?”

“She wants us to write about the different colours of the rainbow – ‘ _bananas are like the yellow in the rainbow’ –_ like I’m five year old,” Sherlock explained, disgust clear in his tone. “A solution of potassium iodide is like pee which I thought would be appropriate. So how much water do I need?”

By now, Mycroft had moved onto the following question to state the _de Broglie_ equations. “Perhaps you might want to describe it as the colour of weak tea, Sherlock, lest you receive a detention.”

Sherlock took two steps in the room. “The answer, Mycroft?” he demanded.

Eager to be rid of his brother, and knowing there were no potassium iodide pills to be found in the house, Mycroft conceded. “Around a hundred-and-forty grams dissolved in a hundred grams of distilled water, Sherlock.”

“Are you sure?”

Tilting his head so he could see Sherlock from the corner of his eye and arched an eyebrow. His brother flushed much to his satisfaction. “If you’re satisfied, I’d rather like to finish this,” he said gesturing to his desk, “as soon as possible.”

“Whatever,” Sherlock spat back, before hurrying out and slamming Mycroft’s bedroom door behind him.

Mycroft sighed as he continued to answer the remainder of the homework assigned ahead of his mock A-Level Physics exam later that November. He felt a strange urgency, a nagging feeling. It wasn’t an uncommon occurrence given he lived under the same roof as Sherlock, whose unpredictability at the age of ten kept Mycroft on his toes all too often.

Suddenly the reason for his agitation came to him. The potassium iodide. In pill form. _Mad_ Uncle Eugene who thought that the USSR would drop a nuclear bomb in the country at any given moment. Or one of the country’s nuclear reactors would go critical.

Uncle Eugene who had stockpiled quite a supply of potassium iodide pills for such an emergency.

Their Uncle Eugene who they had visited just the weekend before last.

Mycroft dropped his fountain pen, ignoring the splatter of ink that spilled across his homework, pushing away from his desk and hurried downstairs. There was only one place where Sherlock would be. The kitchen.

As expected, as feared, Sherlock had set up his paraphernalia, substituting Mummy’s kitchen utensils where needed. There was obvious evidence of some sort of colourful experiment if the kitchen sink was any indication. Perhaps there was some truth to Sherlock’s claim to homework on the colours of the rainbow.

The lightly scorched wooden tongs meant Sherlock had used the gas cooker in lieu of a Bunsen burner without supervision. The little _brat_ had obviously been up to mischief for at least an hour, if not longer.

Mummy would be furious.

If he wasn’t quite so horrified, Mycroft might have considered himself a little impressed at his little brother’s ingenuity. “Sherlock,” he thundered. “What in god’s name do you think you’re doing?”

“What does it look like?”

Mycroft looked. Sherlock was stirring the liquid in one of their large vases using the knife sharpener, the only implement that was both long and narrow enough to fit the container’s narrow neck. The vase, one that normally held a collection of flowers from their garden that Dad collected every few days for Mummy. Only it had been divested of flowers and instead held a pale brown coloured liquid. At least a quart of liquid. _The potassium iodide solution._

Mycroft cast wider and as he _saw_ his eyes grew wider in disbelief. There near the kitchen door was the large container of hydrogen peroxide his father used in their garden, mostly as fertiliser. There were multi-coloured drops of Mummy’s food colouring on the kitchen table, probably still out from making Daddy’s birthday cake just a few days before.

And Mycroft could clearly see that the cylindrical white Fairy liquid bottle sitting next to the filthy sink bore the marks of Sherlock’s messy, colourful, fingerprints. By the new dents in the bottle, he estimated at least a quarter of the cleaning liquid had been appropriated.

He turned his gaze back onto Sherlock, who was leaning over one of the garden containers he’d dragged into the kitchen, the vase containing the potassium iodide in hand. “Stand back, Sherlock! You could get hurt!”

“The term you should be using is exothermic.”

Mycroft huffed at the snotty tone his brother affected. “Yes, thank you. I know that but I’m much more concerned that you’ll burn yourself standing so close.”

“Concerned, Mycroft?”

“With your particular set of destructive qualities, brother mine, who wouldn’t,” Mycroft parried. “Step back at once!”

“What for?”

“Because Mummy will be furi-“

Mycroft didn’t get to finish his sentence because Sherlock, insolent and inquisitive, poured the solution in his hand into the second container before jumping back. His shorter, bonier body bumped into Mycroft, who grabbed Sherlock and tried to pull him back from the expectant explosion.

And explode it did.

Sherlock had, in his infinite stupidity, decided to recreate the _elephant toothpaste_ experiment in the family kitchen. Except with higher strength chemicals and bigger volumes.

“Wow! Look Mycroft!”

It truly was a spectacular reaction. The coloured ‘foam’ – really a chemical reaction that resulted in small bubbles exploding from the narrow neck of its container – hit the kitchen ceiling several times from the pressure of the exothermic reaction. And continued to bubble, grow and expand all over the floor.

“Oh dear lord,” Mycroft groaned.

“Isn’t it cool,” Sherlock continued. He was practically vibrating in Mycroft’s embrace. “Stupid dull teacher wouldn’t let me do this at school. Too dangerous.”

“For good reason!”

Sherlock made a rude noise before twisting out of Mycroft’s grip. Before he could stop his little brother, he’d taken the few steps into the still expanding mess of foam, dirtying his clothes and clothes. Mycroft closed his eyes for a moment and took a deep breath but when he opened his eyes again, the kitchen in its current state of disarray still stood before him.

He’d just started on a plan to clean and tidy up the kitchen as best possible, with Sherlock’s help willing or not, when the inevitable happened. Their parents had come back.

“Oh my god!” “Oh dear.”

“It was Mycroft!” Sherlock, the little sneak. He was hit by the sudden urge to smack his horrendous excuse of a brother once – even in front of his parents.

“What, how?” At any other time, Mycroft would have enjoyed the rare occasion of his mother being lost for words. “ _Mycroft_!”

He flushed and make a snap decision, looked meekly back at his red-faced mother. “I got the concentrations wrong. Sorry.”

“You’re the eldest! How did you two manage to make so much … is that the hydrogen peroxide we keep in the shed? And my colours for the icing. Oh!”

Mycroft ignored the smug look Sherlock threw at him as Mummy buried her face in his father’s shoulder. “Mummy …”

His mother pulled back and Mycroft was relieved to see that she hadn’t been crying. “Stop. Both of you go upstairs and get changed and come back down,” she ordered. “You created this mess, you _will_ clean it up.”

“But Mummy, I have homework and mock exams-“

“No excuses, Mycroft. You made the mess, you clean it up. House rules.”

Mycroft barely caught himself before rolling his eyes, saving himself from a second scolding. “Come on,” he said to Sherlock, adding, “brat,” under his breath. Defeated, knowing there was no arguing with his mother, he gave her and his father a wide berth as he made to leave the kitchen.

As he trudged towards the stairs, Sherlock in his wake, not nearly as disappointed as Mycroft had hoped – the thrill of the spectacular explosion of foam no doubt – he heard his father comfort Mummy.

“Don’t worry dear. We’ll redecorate the kitchen. You always wanted to have a more homely-feeling place, my love.”

“But the boys.”

“Are just being inquisitive, dear. Perhaps I might want to clear out some of the space in the shed?”

He didn’t hear what reply Mummy made to the suggestion because at that moment Sherlock decided to speak. Voice still bubbling with exhilaration.

“Mycroft, do you know where I could get some liquid nitrogen? Malcom is an idiot but his father is a physicist apparently and he told me his Daddy can make ice-cream from milk, cream, sugar, eggs and liquid nitrogen.”

“Sherlock,” Mycroft tried in a warning tone.

“So will you get me some liquid nitrogen, Mycroft?” Sherlock asked again, throwing his most innocent looking, wide-eyed face at him. As if not only minutes ago he hadn’t just sullied the kitchen with an explosion of multi-coloured foam.

Mycroft realised at that moment he was going to have to plan to save himself from Sherlock. Protect innocent bystanders. And most importantly, protect Sherlock from himself.


End file.
